Patent Application
20090085087
The invention generally relates to a structure used to enhance the integrity of devices formed on a semiconductor wafer. More particularly, the invention relates to a structure used to enhance the integrity of devices formed generally perpendicular to a semiconductor wafer.
Devices made from semiconductor materials are used to create memory circuits in electrical components and systems. Memory circuits are the backbone of such devices as data and instruction sets are stored therein. Minimizing the amount of natural resources and space consumed by memory circuits is a primary motivation in the designing of such circuits. As the design of memory circuits has moved from two-dimensional designs to three-dimensional designs, more emphasis is being made to minimize the space required to build structures, while maintain the integrity and strength of same, which becomes more important as more elements are incorporated into a space, the greater the cost in having to replace that component should one element therein fail.
Electrical connections between dielectric layers and electrical components of an integrated circuit are required to be strong. Likewise, the electrical components themselves must be strong enough to endure harsh environmental conditions during continued manufacturing processes and a subsequent use life. Therefore, the connections between the electrical components and the wafer must be strong.
Countering the principal of strength is the requirement to make electrical components smaller and more compact with respect to each other. As the electrical component gets smaller to accommodate the compression requirements, the electrical component is weakened. Hence, the ability to maintain the electrical component on the semiconductor wafer is reduced, resulting in a higher rate of failure.
A semiconductor wafer assembly includes a base of dielectric. A layer of silicon is deposited thereover. A metal hard mask is deposited over the silicon. A dielectric hard mask is deposited over the metal hard mask. Photoresist is deposited over the dielectric hard mask, whereby a plurality of sacrificial columns is formed from the layer of metal hard mask through the photoresist such that the sacrificial columns extend out from the silicon layer. An interface layer is disposed between the layer of conductive material and the layer of hard mask to enhance adhesion between each of the plurality of sacrificial columns and the layer of conductive material to optimize the formation of junction diodes out of the silicon by preventing the plurality of sacrificial columns from being detached from the layer of silicon prematurely.
Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
a through 3d are cross-sectional side views illustrating steps in the process of forming conductive rails by a subtractive method;
a through 4d are cross-sectional side views illustrating steps in the process of forming conductive rails by a Damascene method; and
a through 5g are cross-sectional side views of a semiconductor wafer through the steps in the process of forming elements using the invention.
Referring to
The term junction diode is used herein to refer to a semiconductor device with the property of non-ohmic conduction, having two terminal electrodes, and made of semiconducting material which is p-type at one electrode and n-type at the other. Examples include p-n diodes and n-p diodes, which have a p-type semiconductor material and an n-type semiconductor material in contact, such as Zener diodes, and p-i-n diodes, in which an intrinsic (undoped) semiconductor material is interposed between the p-type semiconductor material and the n-type semiconductor material.
In the initial state of the memory cell 20 of
Referring to
Features in semiconductor devices such as the memory cell 20 are generally formed either by subtractive or by Damascene methods. In a subtractive method, a material is patterned and etched into a desired shape. Gaps are then etched between features and filled with dielectric. In a Damascene method, features are formed by forming voids in dielectric, then filling those voids with conductive or semiconductor material.
For example, to form metal rail-shaped conductors using the subtractive method, as shown in
To contrast the example shown in
In the embodiment of the '030 patent, shown in
The junction diodes 22 extend generally between these two conductors 26, 28 (there may be layers intermediate between the junction diodes 22 and the two conductors 26, 28). The junction diodes 22 are prone to fail due to should a portion of a photoresist or hard mask layers fail to adhere or peel during the fabrication steps. This failure may occur during the etching and forming steps. In the embodiment shown in
A hard mask is an etched layer that serves to pattern the etch of an underlying layer(s); if all of the photoresist has been consumed, the layers of hard mask 54, 58 can provide the pattern in its stead. The use of porous low-k layers, in addition to the reduced dimensions of electrical components being fabricated, requires the presence of the metal hard mask 58. A metal hard mask 58 provides the best protection against resist poisoning, and works well for the porous low-k films. In the embodiment shown, a layer of dielectric anti-reflective coating 60 (DARC) may be used to facilitate the fabrication of the junction diodes 22. The DARC layer 60 prevents off-axis erosion of the photoresist layer 56 that may otherwise occur during subsequent processing steps due to the reflection of light in the etching process.
Below the layer of metal hard mask 58 is a layer of interface material 62. Because the metal hard mask 58, dielectric hard mask 54 and photoresist 56 layers are required for a plurality of fabrication steps, they tend to break away from the silicon layers, discussed subsequently, that are being formed into the junction diodes 22. This results in the failure of forming the pillar structures thereunder. The interface layer 62 is a thin adhesive layer that is applied to the structure between the dielectric 54 and metal 58 hard mask layers. The interface layer 62 provides sufficient adhesion to prevent the etched hard mask and photoresist from breaking from the layer of metal hard mask layer 58. The interface layer 62 adheres or glues the dielectric hard mask layer 54 to the metal hard mask layer 58 during subsequent fabrication, which enhances the productivity and quality of the memory device being manufactured. Because the interface layer 62 is conductive, it and the metal hard mask layer 58 may remain in or on the device without affecting the performance of the memory device being manufactured, should it be desired to leave it or ignore it during subsequent processing steps. The interface layer 62, fabricated from titanium nitride or tungsten nitride using standard reactive PVD and/or CVD methods, will be discussed in greater detail subsequently.
Below the layer of metal hard mask 58 is a layer of adhesive 64 which aids in the adhesion between the layer of metal 58 and a layer of antifuse material 66, disposed below the layer of metal hard mask 58. The layer of antifuse material 66 is used for the purpose of forming the dielectric rupture antifuse 24, discussed above. In many embodiments, the material used to create the layer of adhesive 64 between the layer of metal hard mask 58 and the layer of antifuse material 66 is TiN.
Directly below the layer of antifuse material 66 are three layers of silicon 68, 70, 72. The three layers of silicon 68, 70, 72 include the heavily doped layer of silicon 68, an intermediate layer of silicon 70, which is undoped or lightly doped, and another heavily doped layer of silicon 72. Each of these layers 68, 70, 72 are used in the fabrication of the heavily doped semiconductor layer 30, intermediate layer 32 and heavily doped semiconductor layer 34, all of which form the vertically oriented junction diode 22, discussed in greater detail above. A subsequent layer of adhesive 74, typically TiN, is deposited below the layers of silicon 68, 70, 72.
The bottom of the device includes a layer of conductors 28. The conductors 28 are fabricated from tungsten, or an alloy thereof, and are fabricated using one of the methods discussed above. Spacers 78, made of an inert material such as silicon dioxide, separate the conductors from each other. While the bottom layer of adhesive 74 may extend between each of the conductors 28 and spacers 78, it is typically not present unless the layer of conductors 28 are fabricated using the Damascene method.
The structure described above in the paragraphs immediately preceding is the structure that will be used to form the junction diodes 22. The first step of the fabrication process is shown in
Referring to
The addition of an interface layer 62 to maintain the sacrificial columns 82 in place is counter-intuitive because the sacrificial columns 82 are eventually removed. But, premature removal, for whatever reason, reduces the effectiveness and efficiency of the production pillars or junction diodes 22. The interface layer 62 increases the efficiency of production while allowing for subsequent removal of the sacrificial columns 82.
The thickness of the interface layer 62 may be in a range between five and ten nanometers, inclusive. The range of widths of the pillars after the clean portion of the fabrication process may be between 53 nm and 69 nm when the interface layer 62 is fabricated from titanium nitride. With respect to this example of the invention, the titanium nitride interface layer 62 may have a ratio of titanium and nitrogen as approximately 1:1. None of the junction diodes 22 fell from the hard mask layer 54 and peeling did not occur.
The thickness of the interface layer 62 may be in a range between five and ten nanometers, inclusive. The range of the widths of the pillars after the clean portion of the fabrication process may be between 72 nm and 80 nm when the interface layer 62 is fabricated from tungsten nitride. In this example, a nitrogen flow of 43% was present. None of the junction diodes 22 fell from the hard mask layer 54 and peeling did not occur.
Referring to
After the metal hard mask 58 has been etched, the junction diodes 22 are formed, as is shown in
Once the junction diodes 22 and the dielectric rupture antifuses are formed, there is no longer any need for the sacrificial columns 82. These are removed using traditional ash methods. Referring to
Referring to
Once the junction diodes 22 have been created in pillar form (similar to those shown in
Throughout this description, one layer has been described as being “above” or “below” another. It will be understood that these terms describe the position of layers and elements relative to the substrate upon which they are formed, in most embodiments a monocrystalline silicon wafer substrate; one feature is above another when it is farther from the wafer substrate, and below another when it is closer. Though clearly the wafer, or the die, can be rotated in any direction, the relative orientation of features on the wafer or die will not change. In addition, the widths of the layers shown are not to scale and are only shown here for illustrative purposes.
The methods for forming the conductors are more fully disclosed in a patent application entitled “Conductive Hard Mask to Protect Patterned Features During Trench Etch,” having U.S. Ser. No. ______, assigned to the assignee of the present invention, the disclosure in which is hereby incorporated by reference.
The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.
Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.
